1. Field of the Invention
This invention relates to light emitting diode (LED) packages and more particularly to side-emitting LEDs.
2. Description of Related Art
As illustrated in FIG. 1, many light sources, including many light emitting diode (LED) semiconductor die, produce light in a Lambertian radiation pattern with respect to an axis perpendicular to the base plane of the die. The majority of the light leaving the die is substantially forwardly directed, although much of it is at a wide angle. Many applications, however, require substantially all light to be directed at a wide angle, approaching or somewhat exceeding 90°, with little or no light at forward angles.
In order to obtain a wide angle distribution of light from an LED package, a side-directing lens configured to redirect light may be added to the LED package. FIG. 2 illustrates a known LED package with such a lens. The LED package includes an LED chip, a lens with straight vertical sidewalls and a funnel-shaped top surface. There are two main paths in which light travels through the package. The first light path P1 is desirable. The light emitted from the chip travels to the top surface where total internal reflection (TIR) causes the light to exit through the sidewall at approximately 90° to the longitudinal axis. The second light path P2 is light emitted from the chip towards the sidewall at an angle that causes TIR or reflection from the sidewall toward the top surface at an angle that allows the light to exit through the top surface. This path is not desirable and limits the efficiency of side extracted light.
U.S. Pat. No. 6,607,286 discloses such another side-directing lens. The lens, which is shown in FIG. 3, includes a sawtooth, refractive portion and a top funnel portion. The sawtooth portion is intended to refract and bend light so that the light exits the lens close to 90° with respect to the longitudinal axis of the LED. The sawtooth feature of this lens, however, makes the lens difficult to manufacture. For example, during an injection molding process, the undercuts of the sawtooth feature necessitate a side action injection mold.